In a recycling center, plastic household bottles arrive in a wide variety of colors; an inspection of the shelves in a supermarket will provide a preview of what will be found in the recycling center. The bottles that arrive at the center are then shredded into tiny pieces (approximately 2 mm..times.2 mm.) which have the labels still attached. Thus, after shredding, a single bottle will be divided into hundreds of pieces. While the color of each piece might be uniform, where the bottles are to be separated by color after shredding it is necessary to perform a color measurement of each of the individual pieces. Further, the small segments also will present material handling problems. Therefore, it is clearly desirable to detect the color of the plastic bottle before the bottle is shredded, so that the bottles may be sorted as to color before shredding. However, the use of an automated system to detect bottle color presents an obvious problem: a bottle made of a particular color plastic may have a label of a second color with lettering of a third color. In fact, the desire on the part of the manufacturer to catch the eye of the consumer usually results in there being many different colors on the label.
There are a number of different methods for detecting the color of an object and some of these methods are disclosed in the patents discussed below.
U.S. Pat. No. 4,488,245 (Dalke et al.) discloses a process for color detection wherein the recognition of color is based on the definition of a three-dimensional color subspace. The brightness and luminance of are used to determine a color value. This color value is then digitized. The digitized value is then compared to patterns which define the different color sub-spaces.
U.S. Pat. No. 4,714,955 (Nishimura et al.) discloses a color camera having several selective filters for passing specific wavelengths of light. The output of the filters are fed into an algorithm to determine the primary color, e.g. Red, Green, and Blue (RGB) components of the original object.
U.S. Pat. No. 4,718,089 (Hayashi et al.) discloses a video camera that views an object. The signal corresponding to the object is then processed so as to separate the luminance signal from the image signal. Two color signals are then compared to the signal to determine whether the luminance signal falls within an acceptable range. If the luminance signal is within the range, then there is a logical "0" generated, else a logical "1" is generated. The ability to determine the luminance is only one part in determining the "color" of an object and the presence of a label on the object would provide false luminance information.
U.S. Pat. No. 4,812,904 (Maring et al.) discloses an optical color analysis process which employs a camera which takes a picture of an object. This picture is then digitized. The digitized picture is then broken down into component RGB values and is compared with a reference signal to determine if they are statistically similar.
U.S. Pat. No. 4,907,075 (Braudaway) discloses a system comprising a video camera, a computer, and a display. The video camera takes a digitized picture of an object located below the camera. Then this digitized picture is divided into pixels. Each pixel is identified with a specific color and intensity. An overall color is generated by parsing each pixel and determining the centroid color, the color having the greatest number of pixels. This color is then used as the base color of the object. This method of determining color is inaccurate if the object is moving.
U.S. Pat. No. 4,979,029 (Lemelson) discloses a system that incorporates a video camera that is used to detect colors and/or shapes. The system then performs actions based on the detection of specific colors or shapes.
A major disadvantage of the methods and systems described above is that they are generally not suitable for use in determining the color of an object having a label of a different color attached thereto. Further, in some instances, the methods and systems are unable to detect the color of a moving object.